Printed chemical mechanical polishing pad having controlled porosity

ABSTRACT

A method of fabricating a polishing pad includes determining a desired distribution of voids to be introduced within a polymer matrix of a polishing layer of the polishing pad. Electronic control signals configured to be read by a 3D printer are generated which specify the locations where a polymer matrix precursor is to be deposited, and specify the locations of the desired distribution of voids where no material is to be deposited. A plurality of layers of the polymer matrix corresponding to the plurality of the first locations is successfully deposited with the 3D printer. Each layer of the plurality of layers of polymer matrix is deposited by ejecting a polymer matrix precursor from a nozzle. The polymer matrix precursor is solidified to form a solidified polymer matrix having the desired distribution of voids.

CLAIM OF PRIORITY

This application claims priority under 35 USC §119(e) to U.S. patentapplication Ser. No. 61/919,578, filed on Dec. 20, 2013, the entirecontents of which are hereby incorporated by reference.

TECHNICAL FIELD

This present invention relates to polishing pads used in chemicalmechanical polishing.

BACKGROUND

An integrated circuit is typically formed on a substrate by thesequential deposition of conductive, semiconductive, or insulativelayers on a silicon wafer. A variety of fabrication processes requireplanarization of a layer on the substrate. For example, for certainapplications, e.g., polishing of a metal layer to form vias, plugs, andlines in the trenches of a patterned layer, an overlying layer isplanarized until the top surface of a patterned layer is exposed. Inother applications, e.g., planarization of a dielectric layer forphotolithography, an overlying layer is polisshed until a desiredthickness remains over the underlying layer.

Chemical mechanical polishing (CMP) is one accepted method ofplanarization. This planarization method typically requires that thesubstrate be mounted on a carrier head. The exposed surface of thesubstrate is typically placed against a rotating polishing pad. Thecarrier head provides a controllable load on the substrate to push itagainst the polishing pad. A polishing liquid, such as slurry withabrasive particles, is typically supplied to the surface of thepolishing layer.

One objective of a chemical mechanical polishing process is polishinguniformity. If different areas on the substrate are polished atdifferent rates, then it is possible for some areas of the substrate tohave too much material removed (“overpolishing”) or too little materialremoved (“underpolishing”).

Conventional polishing pads include “standard” pads and fixed-abrasivepads. A standard pad has a polyurethane polishing layer with a durableroughened surface, and can also include a compressible backing layer. Incontrast, a fixed-abrasive pad has abrasive particles held in acontainment media, and can be supported on a generally incompressiblebacking layer.

Polishing pads are typically made by molding, casting or sinteringpolyurethane materials. In the case molding, the polishing pads can bemade one at a time, e.g., by injection molding. In the case of casting,the liquid precursor is cast and cured into a cake, which issubsequently sliced into individual pad pieces. These pad pieces canthen be machined to a final thickness. Grooves can be machined into thepolishing surface, or be formed as part of the injection moldingprocess.

In addition to planarization, polishing pads can be used for finishingoperations such as buffing.

SUMMARY

The material properties of the polishing pad have an effect onpolishing. The porosity in the bulk of a polishing layer affects itscompressibility, and the porosity at the surface of the polishing layercan contribute to slurry distribution. Porosity can be measured as thepercentage volume of voids in the material.

Typically porosity in the polishing layer is introduced by including amaterial different from the pad material into the polishing pad.However, at the interface between the pad material and the differentmaterial, the differences in the hardness of the two materials can causesecondary scratches on a substrate that is being polished.

In some polishing layers, gas bubbles are injected into the liquidprecursor to create voids. It is difficult to achieve uniform localdistribution of gas bubbles, which can lead to differences in hardnessacross different regions of the polishing layer. The variations in padhardness can impact the within-wafer uniformity of the polishedsubstrate substrates. Conventionally, grooves are machined into thepolishing layer to aid the transport of slurry along the polishingsurface of the pad. However, the profiles of the grooves in thepolishing layers are limited by the milling, lathing or machiningprocesses. In addition, fibers of the polishing layer material mayremain on the side of the groove after milling. These machining fibersmay cause local resistance to the slurry flow.

3D printing allows better control of the distribution of pores in thepolishing layer. Alternatively or in addition, 3D printing can be usedto produce specific grooves profiles and/or reduce (e.g., eliminate)fibers within grooves that result from conventional machining of thepolishing layer.

In one aspect, a method of fabricating a polishing pad includesdetermining a desired distribution of voids to be introduced within apolymer matrix of a polishing layer of the polishing pad, and generatingelectronic control signals configured to be read by a 3D printer. Thecontrol signals specify a plurality of first locations where a polymermatrix precursor is to be deposited, and specify a plurality of secondlocations corresponding to the desired distribution of voids where nomaterial is to be deposited. A plurality of layers of the polymer matrixcorresponding to the plurality of the first locations is successivelydeposited with the 3D printer, each layer of the plurality of layers ofpolymer matrix being deposited by ejecting the polymer matrix precursorfrom a nozzle. The polymer matrix precursor is solidifyied to form asolidified polymer matrix having the desired distribution of voids.

Implementations may include one or more of the following features.

Determining the desired distribution of voids may include determiningone or more parameters selected from the group consisting of the size ofthe voids, and the spatial location of the voids within the polymermatrix.

The one or more parameters may be selected to compensate for differentlinear velocities of the polishing pad on a rotating polishing platen.

Printing on selected areas of the polishing layer may be performed toform grooves in a top surface of the polishing layer, wherein thegrooves comprises regions where no polymer matrix precursor isdeposited.

The grooves may have different depths across the top surface of thepolishing layer.

The grooves may connect the distribution of voids in a first pattern toform a network of channels configured to transport slurry.

Solidifying the polymer matrix precursor may include curing the polymermatrix precursor in situ after it has been dispensed from the 3D printerand before the polymer matrix precursor is deposited at an adjoiningposition in the layer.

Curing the polymer matrix precursor may include ultraviolet (UV) orinfrared (IR) curing.

The polymer matrix precursor may include a urethane monomer.

The solidified polymer matrix may include polyurethane.

A second desired distribution of voids to be introduced within a polymermatrix of a backing layer of the polishing pad may be determined.

The second desired distribution of voids in the polymer matrix of thebacking layer may be different from the desired distribution of voids inthe polishing layer of the polishing pad.

The second desired distribution of voids in the polymer matrix of thebacking layer may have a higher density of voids such that the backinglayer is more compressible than the polishing layer.

A material of the polymer matrix of the polishing layer may be differentfrom a material of the polymer matrix of the backing layer.

A second plurality of layers may be successively deposited with the 3Dprinter to form the backing layer.

The polishing layer may be printed directly on the backing layer by the3D printer without the use of an intermediate adhesive layer such thatthe polishing layer is bonded directed to the backing layer.

The voids may have dimension of between 30-50 microns.

In another aspect, a method of fabricating a polishing pad includessuccessively depositing a plurality of layers with a 3D printer, eachlayer of the plurality of polishing layers including a polishingmaterial portion and a window portion, the polishing material portiondeposited by ejecting a polishing material precursor from a first nozzleand solidifying the polishing material precursor to form a solidifiedpolishing material, the window portion deposited by ejecting a windowprecursor from a second nozzle and solidifying the window precursor toform a solidified window.

Implementations may include one or more of the following features.

Curing of the polishing material precursor and the window precursor mayform polymer matrixes having the same composition.

The polishing material precursor may include opacity-inducing additivesand the window precursor may lack such additives.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1A is a schematic cross-sectional side view of an example polishingpad.

FIG. 1B is a schematic cross-sectional side view of another examplepolishing pad.

FIG. 1C is a schematic cross-sectional side view of yet another examplepolishing pad.

FIG. 2 is a schematic side view, partially cross-sectional, of achemical mechanical polishing station.

FIG. 3A is a schematic cross-sectional side view illustrating anexemplary 3D printer used to fabricate a polishing pad.

FIG. 3B is a schematic cross-sectional side view illustrating apolishing layer having a pore formed by 3D printing.

FIG. 3C is a schematic cross-sectional side view of an exemplary 3Dprinter having an in situ curing light source.

FIG. 3D is a schematic cross-sectional side of a groove in an exemplarypolishing layer.

FIG. 3E is a schematic cross-sectional side of a groove having machiningfibers in an exemplary polishing pad.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

Referring to FIG. 1A-1C, a polishing pad 18 includes a polishing layer22. As shown in FIG. 1A the polishing pad can be a single-layer pad thatconsists of the polishing layer 22, or as shown in FIG. 1C the polishingpad can be a multi-layer pad that includes the polishing layer 22 and atleast one backing layer 20.

The polishing layer 22 can be a material that is inert in the polishingprocess. The material of the polishing layer 22 can be a plastic, e.g.,a polyurethane. In some implementations the polishing layer 22 is arelative durable and hard material. For example, the polishing layer 22can have a hardness of about 40 to 80, e.g., 50 to 65, on the Shore Dscale.

As shown in FIG. 1A, the polishing layer 22 can be a layer ofhomogeneous composition, or as shown in FIG. 1B the polishing layer 22can include abrasive particles 28 held in a matrix 29 of plasticmaterial, e.g., polyurethane. The abrasive particles 28 are harder thanthe material of the matrix 29. The abrasive particles 28 can be from0.05 wt % to 75 wt % of the polishing layer. For example, the abrasiveparticles 28 can be less than 1 wt % of the polishing layer 22, e.g.,less than 0.1 wt %. Alternatively, the abrasive particles 28 can begreater than 10 wt % of the polishing layer 22, e.g., greater than 50 wt%. The material of the abrasive particles can be a metal oxide, such asceria, alumina, silica or a combination thereof.

In some implementations, the polishing layer includes pores, e.g., smallvoids. The pores can be 50-100 microns wide.

The polishing layer 18 can have a thickness D1 of 80 mils or less, e.g.,50 mils or less, e.g., 25 mils or less. Because the conditioning processtends to wear away the cover layer, the thickness of the polishing layer22 can be selected to provide the polishing pad 18 with a usefullifetime, e.g., 3000 polishing and conditioning cycles.

On a microscopic scale, the polishing surface 24 of the polishing layer22 can have rough surface texture, e.g., 2-4 microns rms. For example,the polishing layer 22 can be subject to a grinding or conditioningprocess to generate the rough surface texture. In addition, 3D printingcan provide small uniform features, e.g., down to 30 microns.

Although the polishing surface 24 can be rough on a microscopic scale,the polishing layer 22 can have good thickness uniformity on themacroscopic scale of the polishing pad itself (this uniformity refer tothe global variation in height of the polishing surface 24 relative tothe bottom surface of the polishing layer, and does not count anymacroscopic grooves or perforations deliberately formed in the polishinglayer). For example, the thickness non-uniformity can be less than 1mil.

Optionally, at least a portion of the polishing surface 24 can include aplurality of grooves 26 formed therein for carrying slurry. The grooves26 may be of nearly any pattern, such as concentric circles, straightlines, a cross-hatched, spirals, and the like. Assuming grooves arepresent, then the polishing surface 24, i.e., the plateaus between thegrooves 26, can be about i.e., can be 25-90% of the total horizontalsurface area of the polishing pad 22. Thus, the grooves 26 can occupy10%-75% of the total horizontal surface area of the polishing pad 18.The plateaus between the grooves 26 can have a lateral width of about0.1 to 2.5 mm.

In some implementations, e.g., if there is a backing layer 20, thegrooves 26 can extend entirely through the polishing layer 22. In someimplementations, the grooves 26 can extend through about 20-80%, e.g.,40%, of the thickness of the polishing layer 22. The depth of thegrooves 26 can be 0.25 to 1 mm. For example, in a polishing pad 18having a polishing layer 22 that is 50 mils thick, the grooves 26 canhave a depth D2 of about 20 mils.

The backing layer 20 can be softer and more compressible than thepolishing layer 22. The backing layer 20 can have a hardness of 80 orless on the Shore A scale, e.g., a hardness of about have a hardness of60 Shore A. The backing layer 20 can be thicker or thinner or the samethickness as the polishing layer 22.

For example, the backing layer can be an open-cell or a closed-cellfoam, such as polyurethane or polysilicone with voids, so that underpressure the cells collapse and the backing layer compresses. A suitablematerial for the backing layer is PORON 4701-30 from Rogers Corporation,in Rogers, Conn., or SUBA-IV from Rohm & Haas. The hardness of thebacking layer can be adjusted by selection of the layer material andporosity. Alternatively, the backing layer 20 formed from the sameprecursor and have the same porosity as the polishing layer, but have adifferent degree of curing so as to have a different hardness.

Turning now to FIG. 2, one or more substrates 14 can be polished at apolishing station 10 of a CMP apparatus. A description of a suitablepolishing apparatus can be found in U.S. Pat. No. 5,738,574, the entiredisclosure of which is incorporated herein by reference.

The polishing station 10 can include a rotatable platen 16 on which isplaced the polishing pad 18. During a polishing step, a polishing liquid30, e.g., abrasive slurry, can be supplied to the surface of polishingpad 18 by a slurry supply port or combined slurry/rinse arm 32. Thepolishing liquid 30 can contain abrasive particles, a pH adjuster, orchemically active components.

The substrate 14 is held against the polishing pad 18 by a carrier head34. The carrier head 34 is suspended from a support structure, such as acarousel, and is connected by a carrier drive shaft 36 to a carrier headrotation motor so that the carrier head can rotate about an axis 38. Therelative motion of the polishing pad 18 and the substrate 14 in thepresence of the polishing liquid 30 results in polishing of thesubstrate 14.

Pad hardness and other material properties of the polishing layer havean effect on the polishing operation. Pad hardness is determined by thematerial used to fabricate the polishing layer, the extent anddistribution of porosity in the polishing layer, and the degree ofcuring used to cure the polymer matrix precursor.

Control of the extent and distribution of porosity offers localizedcontrol of pad hardness. For example, it can be difficult to effectivelyvary the materials (that have different hardness) used to fabricate thepolishing layer spatially across the polishing surface. Similarly, itcan be difficult to control the degree of curing of the pad precursorwith good resolution across the polishing layer. However, as describedbelow, the location and density of pores can be controlled in a 3Dprinting process.

Typically porosity in the polishing layer 22 is introduced by includinga material different from the polymer matrix precursor into thepolishing layer. In some polishing pads, the porosity is introduced byincluding pore-containing (e.g., hollow) particles in the polishinglayer. For example, hollow microspheres of known size can be mixed withthe liquid precursor, which is then cured to form the material for thepolishing layer. However, at the interface between the pad material andthe particles, the differences in the hardness of the two materials cancause secondary scratches on the substrate that is being polished.

In some polishing layers, gas bubbles are used instead of particles tocreate voids. In this way, the need to use particles that are made of amaterial different from that of the polishing layer to create porosityis eliminated. While it is possible to control the overall porosity, itis difficult to control the pore size and distribution of pores when gasbubbles are used. Due to the somewhat random size and location of thegas bubbles, it is difficult to control the distribution of pores andthe local porosity, and this can lead to differences in hardness acrossdifferent regions of the polishing layer. For example, the diameter ofthe bubbles cannot be effectively controlled as the diameter is afunction of the local surface tension. In addition, it is difficult tocontrol the local distribution of gas bubbles, which can lead todifferences in hardness across different regions of the polishing layer,causing variations in pad hardness that can impact the final polishingof wafers.

In some implementations, the polishing pad is manufactured to have auniform distribution of pores.

In some implementations, the polishing pad is manufactured to have adistribution of pores that, due to the resulting differences inpolishing layer hardness, is used to compensate for the differences inthe linear velocity of the polishing pad being higher at the edge (nearthe circumference) of the polishing pad, compared to the center portionof the polishing pad. This difference in polishing speeds across theradius of the polishing pad, when uncorrected, can result indifferential polishing of a substrate as the substrate is polished atdifferent radial positions of the polishing layer.

In some implementations, the polishing pad is manufactured to have adistribution of pores that, due to the resulting differences inpolishing layer hardness, compensate for other sources of non-uniformityin the polishing rate.

In order to effectively control the hardness of the polishing layer,computer simulations can first be used to determine the desired hardnessof the polishing layer at different locations on the polishing layer.Such a simulation produces a hardness profile of the polishing layerthat can be used to for example, compensate for differences in linearvelocity of the polishing pad when it is being rotated. Based on theselected hardness profile, porosities are then distributed accordinglyto achieve the selected profile. The size of the pores, the density andspatial distribution of the pores can be matched to the selectedhardness profile.

3D printing offers a convenient and highly controllable process forobtaining the porosities determined by computer simulations. Referringto FIG. 3A, at least the polishing layer 22 of the polishing pad 18shown in FIGS. 1A-1C is manufactured using a 3D printing process. In themanufacturing process, thin layers of material are progressivelydeposited and fused. For example, droplets 52 of pad precursor materialcan be ejected from a nozzle 54 of a droplet ejecting printer 55 to forma layer 50. The droplet ejecting printer is similar to an inkjetprinter, but uses the pad precursor material rather than ink. The nozzle54 translates (shown by arrow A) across a support 51.

For a first layer 50 a deposited, the nozzle 54 can eject onto thesupport 51. For subsequently deposited layers 50 b, the nozzle 54 caneject onto the already solidified material 56. After each layer 50 issolidified, a new layer is then deposited over the previously depositedlayer until the full 3-dimensional polishing layer 22 is fabricated.Each layer is applied by the nozzle 54 in a pattern stored in a 3Ddrawing computer program that runs on a computer 60.

The support 51 can be a rigid base, or be a flexible film, e.g., a layerof polytetrafluoroethylene (PTFE). If the support 51 is a film, then thesupport 51 can form a portion of the polishing pad 18. For example, thesupport 51 can be the backing layer 20 or a layer between the backinglayer 20 and the polishing layer 22. Alternatively, the polishing layer22 can be removed from the support 51.

A desired distribution of pores can simply be incorporated into thepolishing layer 22 by not depositing the pad precursor material atparticular locations specified by the desired distribution. That is, apore can be formed at a particular location by simply not dispensing thepad precursor material at that particular location.

In 3D printing, the desired deposition pattern can be specified in aCAD-compatible file that is then read by an electronic controller (e.g.,computer) that controls the printer. Electronic control signals are thensent to the printer to dispense the pad precursor material only when thenozzle 54 is translated to the position specified by the CAD-compatiblefile. In this way, the size of the actual pores in the polishing layer22 does not need to be measured, but rather, the instructions containedin the CAD-file that are used to 3D print the material record the exactlocation and size of the porosity to be incorporated into the polishinglayer 22.

FIG. 3B shows a detailed view of a pore 325 that is formed by 3Dprinting. The nozzle 54 deposit a first layer 310 which is made up of aseries of pad precursor portions 311 deposited at the resolution of theprinter containing nozzle 54. Portions 311 are only schematicallydepicted in rectangular form. For a typical high speed printer having aresolution of, for example, 600 dots per inch (dpi), the width of eachportion 311 (e.g., each pixel) can be between 30-50 microns.

After depositing the continuous first layer 310, nozzle 54 is used todeposit a second layer 320. The second layer 320 contains a void 325where the nozzle 54 does not deposit any polymer matrix precursor. Poresof between 30-50 micron can be formed in the second layer 320 by simplynot depositing materials at those locations.

The layer immediately above the portion having the void can develop anoverhang 332 that is directly above the void 325 in the second layer320. The overhang 332 is retained laterally by the surface tension ofthe deposited polymer matrix precursor portion 331, thus preventing theoverhang 332 from collapsing into the void 325. The nozzle 54 thencontinues to deposit polymer matrix precursor portion 333 which includesan overhang 334 that extends above the void 325. Similar to overhang332, the surface tension of the deposited polymer matrix precursorportion 333 prevents the overhang 332 from collapsing in to the void325.

Each of the printed layers 310-330 can be 30-50 micron in thickness.FIG. 3B illustrates the void in rectangular shape, but in general, thepores in the polishing layer can be spherically shaped, or have othergeometries such as cubic or pyramidal. The minimum size of the voids isdetermined by the resolution of the printer.

Alternatively, for pores close to the polishing surface of the padhaving a pore surface that would be abraded during the polishingprocess, a fluid (e.g., water) that is compatible with the polishingprocess can be deposited into the void, e.g., by a second nozzle. Thepad precursor material that is deposited above the void is not misciblewith the fluid and is prevented from collapsing into the void by thepresence of the fluid. During the polishing process, when a portion ofthe pore surface is abraded, the fluid that is used during the polishingprocess is released from the pore and the pore would have thecompressibility of an unfilled pore.

An ultraviolet (UV) or infrared (IR) curable polymer can be used as thepad precursor material to fabricate the polishing layer, eliminating theneed for an oven, required when polishing pads are manufactured usinginjection molding. The fabrication process of the polishing pad can bemoved from the vendor site and be licensed directly to the customer tobe used at the customer site, where the customer can manufacture theexact numbers of pads that is needed.

Solidification of the deposited pad precursor material can beaccomplished by polymerization. For example, the layer 50 of padprecursor material can be a monomer, and the monomer can be polymerizedin-situ by UV curing. For example, UV or IR light sources 360 can bepositioned in close proximity to the nozzle 54, as illustrated in FIG.3C. In this case, in situ curing can be performed immediately after thepad precursor material is dispensed from nozzle 54 so that the depositedmaterial hardens upon deposition at the desired location in thepolishing layer. In addition, the intensity of the UV or IR lightsources can be adjusted so that the in situ curing occurs only to adegree sufficient to provide structural rigidity to the deposited padprecursor material. Alternatively, an entire layer 50 of pad precursormaterial can be deposited and then the entire layer 50 be curedsimultaneously.

In addition to using pad precursor materials that are curable, thedroplets 52 can be a polymer melt that solidifies upon cooling.Alternatively, the printer creates the polishing layer 22 by spreading alayer of powder and ejecting droplets of a binder material onto thelayer of powder. In this case, the powder could include additives, e.g.,the abrasive particles 22.

Grooves

Conventionally, grooves 26 formed in the polishing surface 24 forcarrying slurry within the polishing surface 24 are typically machined.However, the profiles of such grooves are limited by milling, lathing ormachining processes.

By using a 3D printing process, it is possible to create grooves with awide variety of cross-sectional shapes. For example, it may be possibleto create grooves which are narrower at the top than the bottom of thegroove. For example, it would be difficult to achieve a dovetail profile370, as shown in FIG. 3D, for the grooves.

Fibers 380 of the pad material may remain on the side of the groove 24after milling, as shown in FIG. 3C. These machining fibers may causelocal resistance to the slurry flow. 3D printing can reduce (e.g.,eliminate) these fibers.

In addition, the pores can be interconnected in desired patterns withgrooves to enhance slurry transport. Different depths of grooves canalso be fabricated in the polishing layer.

Conventional pads include a hard covering layer (e.g., polishing layer22) secured to a soft subpad (e.g., a backing layer 20) by a pressuresensitive adhesive (PSA). Using 3D printing, multi-layer polishing padscan be built in a single printing operation without the use of anadhesive layer, e.g., PSA. The backing layer 20 can be made by printinga different precursor polymer and/or using the same pad precursorpolymer but increasing the porosity of the printed structure to allowthe backing layer 20 to be softer than the polishing layer 22.Additionally, the backing layer 20 can be provided with a differenthardness than the polishing layer 22 by using a different amount ofcuring, e.g., a different intensity of UV radiation.

A transparent window can be embedded within the polishing layer. Anoptical monitoring system can send and receive light beams through thetransparent window to and from the layer on the substrate being polishedpolishing layer in order to more accurately determine the endpoint inthe polishing of the substrate.

Instead of separately manufacturing the transparent window and thenusing adhesives or other techniques to secure the window into acorresponding aperture formed in the polishing layer, 3D printing allowsthe transparent window to be directly deposited into the polishinglayer. For example, a second nozzle is used to dispense an opticallyclear material (e.g., transparent polymer precursors that are withoutopacity-inducing additives, e.g., hollow microspheres) used to fabricatethe transparent window, while a first nozzle is used to dispense the padprecursor material having voids at specific positions to achieve thedesired porosity. The interface between the transparent window materialand the pad precursor is bonded directly during the printing process andno adhesive is needed. The window can be printed to be uniformly solid,e.g., without porosity.

The 3D printing approach allows tight tolerances to be achieved due tothe layer-by-layer printing approach. Also, one printing system (withprinter 55 and computer 60) can be used to manufacture a variety ofdifferent polishing pads having different desired distributions ofporosity in the polishing layer, simply by changing the pattern storedin the 3D drawing computer program.

Besides tailoring the porosity distribution in a polishing pad used forCMP, the methods and apparatus described herein can also be used tocontrol size of porosity and the distribution of porosity for shockabsorption, sound dampening and the controller thermal management ofparts.

A number of implementations have been described. Nevertheless, it willbe understood that various modifications may be made. For example,either the polishing pad, or the carrier head, or both can move toprovide relative motion between the polishing surface and the substrate.The polishing pad can be a circular or some other shape. An adhesivelayer can be applied to the bottom surface of the polishing pad tosecure the pad to the platen, and the adhesive layer can be covered by aremovable liner before the polishing pad is placed on the platen. Inaddition, although terms of vertical positioning are used, it should beunderstood that the polishing surface and substrate could be held upsidedown, in a vertical orientation, or in some other orientation.

What is claimed is:
 1. A method of fabricating a polishing pad,comprising: determining a desired distribution of voids to be introducedwithin a polymer matrix of a polishing layer of the polishing pad;generating electronic control signals configured to be read by a 3Dprinter; the control signals specifying a plurality of first locationswhere a polymer matrix precursor is to be deposited, and specifying aplurality of second locations corresponding to the desired distributionof voids where no material is to be deposited; successively depositing aplurality of layers of the polymer matrix corresponding to the pluralityof the first locations with the 3D printer, each layer of the pluralityof layers of polymer matrix being deposited by ejecting the polymermatrix precursor from a nozzle; and solidifying the polymer matrixprecursor to form a solidified polymer matrix having the desireddistribution of voids.
 2. The method of claim 1, wherein determining thedesired distribution of voids comprises determining one or moreparameters selected from the group consisting of the size of the voids,and the spatial location of the voids within the polymer matrix.
 3. Themethod of claim 1, comprises printing on selected areas of the polishinglayer to form grooves in a top surface of the polishing layer, whereinthe grooves comprises regions where no polymer matrix precursor isdeposited.
 4. The method of claim 3, wherein the grooves have differentdepths across the top surface of the polishing layer.
 5. The method ofclaim 3, wherein the grooves connect the distribution of voids in afirst pattern to form a network of channels configured to transportslurry.
 6. The method of claim 1, wherein solidifying the polymer matrixprecursor comprises curing the polymer matrix precursor in situ after ithas been dispensed from the 3D printer and before the polymer matrixprecursor is deposited at an adjoining position in the layer.
 7. Themethod of claim 6, wherein curing the polymer matrix precursor comprisesultraviolet (UV) or infrared (IR) curing.
 8. The method of claim 7,wherein the polymer matrix precursor comprises a urethane monomer. 9.The method of claim 1, wherein the solidified polymer matrix comprisespolyurethane.
 10. The method of claim 1, comprising determining a seconddesired distribution of voids to be introduced within a polymer matrixof a backing layer of the polishing pad, wherein the second desireddistribution of voids in the polymer matrix of the backing layer isdifferent from the desired distribution of voids in the polishing layerof the polishing pad.
 11. The method of claim 10, wherein the seconddesired distribution of voids in the polymer matrix of the backing layerhas a higher density of voids than the desired distribution of voids inthe polishing layer such that the backing layer is more compressiblethan the polishing layer.
 12. The method of claim 10, wherein a materialof the polymer matrix of the polishing layer is different from amaterial of the polymer matrix of the backing layer.
 13. The method ofclaim 10, comprising successively depositing a second plurality oflayers with the 3D printer to form the backing layer.
 14. The method ofclaim 13, wherein the polishing layer is printed directly on the backinglayer by the 3D printer without the use of an intermediate adhesivelayer such that the polishing layer is bonded directed to the backinglayer.
 15. The method of claim 1, wherein the voids have dimension ofbetween 30-50 microns.
 16. A method of fabricating a polishing pad,comprising: successively depositing a plurality of layers with a 3Dprinter, each layer of the plurality of polishing layers including apolishing material portion and a window portion, the polishing materialportion deposited by ejecting a polishing material precursor from afirst nozzle and solidifying the polishing material precursor to form asolidified polishing material, the window portion deposited by ejectinga window precursor from a second nozzle and solidifying the windowprecursor to form a solidified window.
 17. The method of claim 16,wherein curing of the polishing material precursor and the windowprecursor form polymer matrixes having a same composition.
 18. Themethod of claim 17, wherein the polishing material precursor comprisesopacity-inducing additives and the window precursor lacks suchadditives.
 19. A system for fabricating a polishing pad, comprising: a3D printer having a first nozzle to eject a polishing material precursorand a second nozzle to eject a window precursor; and a computerconfigured to cause the 3D printer to successively deposit a pluralityof layers by ejecting the polishing material precursor from the firstnozzle and ejecting a window precursor from a second nozzle and witheach layer of the plurality of polishing layers including a polishingmaterial portion and a window portion, such that solidification of thepolishing material precursor forms a solidified polishing material andsolidification of the window precursor forms a solidified window. 20.The system of claim 19, comprising a source for the polishing materialprecursor and a source for the second nozzle, and wherein the polishingmaterial precursor comprises opacity-inducing additives and the windowprecursor lacks such additives.